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Journal of Virology, May 2002, p. 4886-4890, Vol. 76, No. 10
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.10.4886-4890.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Division of Virology, Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794,1 Department of Microbiology, The University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong SAR, China2
Received 2 November 2001/ Accepted 8 February 2002
A/Goose/Guangdong/1/96-like H5N1 influenza viruses now circulating in southeastern China differ genetically from the H5N1 viruses transmitted to humans in 1997 but were their precursors. Here we show that the currently circulating H9N2 influenza viruses provide chickens with cross-reactive protective immunity against the currently circulating H5N1 influenza viruses and that this protective immunity is closely related to the percentage of pulmonary CD8+ T cells expressing gamma interferon (IFN-
). In vivo depletion of T-cell subsets showed that the cross-reactive immunity was mediated by T cells bearing CD8+ and T-cell receptor (TCR)
/ß and that the Vß1 subset of TCR
/ß T cells had a dominant role in protective immunity. The protective immunity induced by infection with H9N2 virus declined with time, lasting as long as 100 days after immunization. Shedding of A/Goose/Guangdong/1/96-like H5N1 virus by immunized chickens also increased with the passage of time and thus may play a role in the perpetuation and spread of these highly pathogenic H5N1 influenza viruses. Our findings indicate that pulmonary cellular immunity may be very important in protecting naïve natural hosts against lethal influenza viruses.
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